Hmm... It should work. I have exactly the same "Browser Cache" settings, and I get no GTmetrix errors for my site. This maybe means that your webhost does not support the mod_expires module (which is required by W3TC's "Browser Cache" feature). I know almost nothing about modules, but here is a description :

"mod_expires module is responsible for setting of the Expires HTTP header and max-age directive of Cache-Control HTTP header in server responses."

You should ask your webhost whether mod_expires is supported. If it's not supported, you'll have to forget about the "Browser Cache" feature. Sorry.

Sorry, I have no experience with sub-domains. It is possibly the cause of the problem. In fact, you can make a test, by moving one or more images from your sub-domain to your main domain. See whether they disappear from the "Leverage browser caching" list. But I can't help you further, because of my lack of knowledge. I hope someone else helps you.

Your failures are mostly subdomains. Any failures for your main domain name are either because you haven't actually deployed your browser cache settings and are in preview mode or because mod_expires or another required module isn't installed or enabled in apache.

for results, most png's but also js and jpg and others have no expiry time.
Interestingly enough when testing on gtmetrix then PageSpeed gives much better results. So is the Google measurement wrong (blasphemy!) or are no expiry times set?